With increasing competition in consumer industry, companies are investing substantially on different characteristics of the packaging of edible products to become eye-catchers for their consumers. Apart from edible products, focus is also on packaging/appearance of other products such as tissue, paper wipes intended for skin, boards, plastics (e.g. plastic children toys), and so forth. The sought-after characteristics of the packaging include color vibrancy, color consistency, transparency, hue, saturation, glossiness, color retention, etc. However, such packaging or appearance involves the use of chemical inks, for instance, formulated with azoic pigments. Azoic pigments include certain impurities such as primary aromatic amines (PAA) having a tendency to migrate from the packaging to the product, either by permeation through the packaging, or by set-off via contact migration. The primary aromatic amines are present on the pigment as residual starting material, or as a degradation product of a starting material. The combination of food type, printed packaging type, ink type, contact time, contact temperature and repeated use can result in the migration of primary aromatic amines from the packaging into the food, potentially harming the end-consumer.
Contamination of the foodstuff from the packaging by primary aromatic amines is tightly regulated by Annex II, § 1 of the European regulation EU/10/2011, known as the PIM or Plastics Implementation Measure, requiring that plastic and multi-layered plastic materials and articles in contact with food may not release primary aromatic amines into the said food, in which a detection limit of 0.01 mg of primary aromatic amines (as their sum) per kg foodstuff is regarded as detection limit.
Also the Swiss government has applied the same restrictions with respect to the migration of primary aromatic amines in the Swiss Ordinance SR817.023.21, in which the scope is further extended to all materials for food contact, incorporating for instance inks, paper, board, regenerated cellulose, silicone, . . . .
One of the conventional arts to circumvent the migration of primary aromatic amines into the foodstuff is to use color indexes i.e. non-azoic pigments, having neither primary aromatic amines as starting material, nor compounds releasing primary aromatic amines by degradation. Some examples of these non-azoic pigments include diketopyrrolopyrrole (DPP), quinophtalone, or inorganic pigments. However, such pigments often do not have the required coloristic properties found on azoic pigments. As an example, inorganic pigments typically have a color strength up to five times lower than azoic pigments, are unable to cover the wide color space as adequately as azoic pigments, and typically, but not generally, have low chroma and low transparency levels with respect to azoic pigments. In addition, non-azoic pigments are typically more expensive than azoic pigments.
Another conventional art discloses UV-curable, low migration inks such as SunCure (Sun Chemical Corporation). Such method involves immobilization of all migratable impurities using advanced crosslinking and netting. However, the method currently limits the applicability of such inks on substrates suitable for UV-curing. Also, UV-curable products are not suitable for small packaging for food for infants and small children as the release of acrylic monomer, photo-initiators or other impurities to infant food, due to incomplete polymerization and subsequent curing, cannot be guaranteed. In addition, UV-curable inks such as the abovementioned SunCure are restricted from use in microwave or ovenable consumable goods or food products which require direct contact with the packaging material. Moreover, the aforementioned method is limited to substrate printing, and has no benefit in f.i. mass coloured plastics such as, but not limiting to, masterbatches.
In another instance disclosed in WO2005105928A1, (Clariant Produkte GmbH), the manufacturing of high purity naphtol AS pigments is disclosed by using microreactors, followed by solvent wash and membrane microfiltration. Such method, though resulting in low residual primary aromatic amine content, requires a tailored set of parameters per pigment production. In addition, the method involves extra cost for production, for example, investments in micro reactors, membranes for purification, and expenditure on ATEX-equipment. The method also requires extra production time as the method requires effectiveness for some thorough steps such as washing of agglomerates by solvent switch, trace solvent removal, solvent recuperation, etc. Furthermore, the said method is only specified for the manufacturing of red naphtol type azoic pigments.
According to another instance as disclosed by WO2009129455A8 (Sun Chemical Corp.), an in situ synthesis of a solid solution of C.I. Pigment Yellow 13 and C.I. Pigment Yellow 83 can improve the primary aromatic amine content as compared to the separate synthesis of C.I. Pigment Yellow 13 and C.I. Pigment Yellow 83. However, PAA content still remains high as 370 ppm calculated as aniline versus a general trend towards a limit lower than 20 ppm of residual primary aromatic amines on the pigment for food contact applications.
According to yet another conventional instance, as disclosed in WO2013066246A1 (Xylophane Aktiebolag), a barrier layer can be incorporated in the substrate to prevent the migration of primary aromatic amines, be it a functional barrier such as polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) or an absolute barrier such as aluminium foil or a metallized plastic. Also, an immobile top coat barrier such as Novaset (Flint Group) can be applied on the printed surface to eliminate contact migration by set-off. However, such barrier increases the overall cost and is limited to only plastic packaging manufacturing or laminated, multi-layered tetra-brik type containers. Furthermore, as disclosed in U.S. Pat. No. 5,116,649 A (Westvaco Corporation), barrier films based on EVOH have little to no adhesion to most polymers and paper, except for nylon, and finally, EVOH resins are sensitive to the effects of moisture, resulting in a reduced barrier performance by increasing relative humidity.
The invention U.S. Pat. No. 4,643,770 describes the reduction of free primary aliphatic fatty amine on pigment preparations for ink applications involving a flushing process. Aliphatic fatty amines are amongst others used as surfactants to improve the compatibility of the water containing pigment press cake with the organic phase used during the flushing process, and to improve the dispersibility of said pigment, optionally by forming a long chain ketamine from the acetoacetyl moiety of the pigment. As typically large molar equivalent excess of fatty amine with respect to the pigment are used, the process yields substantial residual amounts of fatty amines. It is known in the art that excess fatty (di)amine can have detrimental effects on ink formulations, or induce foaming. Abovementioned patent provides a solution by converting only a small part (typically 5 mole percent) of the acetoacetyl moiety of coupling agent to a ketamine prior to pigment synthesis. However, it only considers aliphatic primary amines, and the resulting pigment composition still contains less than one percent of residual aliphatic amine, thus not offering a solution for trace quantities of primary aromatic amines at parts per million level from the pigment synthesis.
As a conclusion, the described examples show that it is difficult to achieve PAA migration free azoic pigment.
Therefore, there exists a need for developing a method for manufacturing azoic pigments free of migration of PAA which is cost saving and effective.